Adjusting a scope

Before I start, just a mention that today marks the first anniversary of this blog! Now, to business.

Scope sights are very common these days, but have you read and understood the instructions that come with them? Many shooters have scopes on their guns that are so far out of whack that it’s a wonder they can see through them at all! Let’s take a look at the basics of adjusting a scope on an air rifle.

Eye relief is importantTo be the most useful, a scope should be positioned so you see as much as possible of the image that exits the eyepiece. This image is called the exit pupil, and you are seeing all of it when the image appears as large as it can be. If you see only a small image surrounded by a lot of scope, you are either too close (unlikely) or too far from the eyepiece, which is common. To fix this, you must loosen the scope in the rings and slide it back (or forward) until your eye sees the best (largest) image. Sometimes, you may also need to move the scope rings, which is why I always use two-piece rings whenever possible. One-piece rings are not as easy to position as two-piece rings.

It’s important that your eye is always in the same place to look through the scope. This helps reduce parallax as much as possible and makes sure the scope is positioned correctly when your eye goes to the right place (as naturally as possible) on the stock. Once the scope is situated so you see the biggest image, you can move on the the next step.

Focus the scopeFocusing a scope does not mean adjusting it to see the target clearly. That adjustment is done by the AO (adjustable objective) and comes later. Focusing the scope means adjusting the eyepiece so you see the reticle clearly. To do that, you need to be looking at a plain background so your eye is not distracted from the image of the reticle. You will find that the eyepiece of the scope rotates in both directions, just like the eyepieces on a pair of quality binoculars. Rotate the eyepiece until the reticle appears sharp, then leave the adjustment there for the rest of the time you use the scope. This adjustment is not used in conjunction with the target – it is applying correction for your eyes. This helps most people use scopes without their glasses, because the scope corrects for their vision. There are a few eye problems a scope cannot correct, so you may still need to wear glasses.

The focus ring on a Leapers scope adjusts for your eye, bringing the reticle into sharp focus. Photo borrowed from the Pyramyd Air article All about scopes. – Part 1.

Here’s a tip for making this adjustment. If you stare at the reticle for a long time, your brain will focus your eyes to make it sharp. So, look through the scope for only a few seconds at a time while making this adjustment. I use a light-colored wall as my backdrop. I look through the scope and adjust the eyepiece, then look away. When I look back, if the reticle is in sharp focus, I’m done. If not, I make another small adjustment. Some inexpensive scopes may not have the eyepiece adjustment. If that’s the case, there is nothing you can do but move on.

Adjusting the parallax adjustment correctlyTankers used to use a device called a coincidence rangefinder to determine the range to a target. Cameras used to have them, too. You look through the eyepiece and see a double image of the target; by turning a dial, the two images come together in sharp focus. The rangefinder uses mechanical triangulation to determine range based on how much the two mirrors must be moved to bring the images together. Sounds great except for one thing. If you are not extremely careful, it is so easy to be off by a few hundred yards and not know it. But I know a trick that will help you do this easier!

The parallax ring on an AirForce scope adjusts by bringing the target into sharp focus. The distance may then be read off the scale, as shown here. Photo borrowed from the Pyramyd Air article All about scopes. – Part 1.

Adjust from both directionsThe trick is to adjust the AO from both directions. Sometimes, you won’t see the target get sharp as easily coming from one direction as you will from the other. If you adjust from both near and far, you will get a thin band of possible range within which the target probably lies. You do everything while looking through the scope and adjusting the AO. Only when you believe you have the range determined correctly do you take your eye off the target to dial in the elevation needed for that distance. This is where you will come to appreciate scopes with sidewheel parallax adjustment, like the one you find on the 30mm Leapers scopes. You can REALLY get precise when that big optional sidewheel is installed!

That’s all there is to adjusting a scope correctly. After you’ve done it a few times, it takes only a few minutes, with the reward of a scope that operates perfectly!

50 thoughts on “Adjusting a scope”

Dear BB, I have a real problem and I realy need your advice.I own a Maxima air rifle and it’s a realy bad drooper for an airgun.A few days ago I have bought a Bushnell Trophy 3-9×40 scope and with this scope mounted on the top of my gun,adjustable mounts are a must.First I need to know what type of adjustable mounts do you advice me to use for my Maxima.Gamo or B-Square adjustable mounts?I fear B-Square won’t fit on the rail of my gun but I need an adjustable mount which has both elevation and side-to-side adjustments.Second, I did a little shimming on the rear mount of my scope,about 1mm,and now I’m worried if I bent my scope.Though my scope is made from an alluminium alloy,very tough, I’m still worried.I fired my air rifle only a couple of dozens of times with the scope installed that way,then I dissassembled the mounts because I was feared not to bend the scope tube.How can you tell if a scope tube is bent or not?

BB.i posted this comment a few days ago, but i post it on an old blog, so i guess u and readers dont get to read it, so i reposted it here, although it’s kinda off topic

U said not to store the 22SG with a pump of air. Why is that?Don’t all pump pneumatic needs a pump of air to keep the valve intact?That brings me to my question. You see, I own an Indonesian made Sharp Innova, it’s quite good really, but it didn’t come with a manual. So do you think I should store my sharp with a pump of air or not? I am quite confused because tha sharp air guns doesn’t work the same way as benjamin sheridan. With sharp airgun, after the pumping , you can shoot right away without cocking the bolt.

or maybe there’s sharp innova owners out there who can give me some advice. jow in md maybe?Haque.

I’m only interrested if there is any type of B-Square adjustable mounts that will fit with a 11-13mm mounting rail.I’m not an american so I don’t have a clue if B-Square’adjustable mounts have a clamp that will fit a 11-13mm mounting rail.

A technique for precise focusing used in astronomy and many other optical areas is to make a mask for the objective with two or three holes (equally spaced). Each hole should be about 1/3 of the diameter of the objective (not critical) and spaced 180 or 120 degrees apart and at the same distance from the center. You should have a mask (piece of cardboard) the diameter of your objective with 2 (or 3) holes.

To focus precisely, put the mask in front of the objective and focus through the eyepiece. You will see two (or three) images if not in focus which will converge to one image when in-focus.

You can extend this somewhat by putting red and green filters over individual holes but that only helps in figuring out if your focus is too close or two far away.

The disadvantage is that this cuts down the light through the scope considerably and it does not work well if you are looking at objects without high-contrast areas.

Yes, B-Square adjustable mounts fit 11-13mm rails. B-Square is the only mont maker who ever measured every popular airgun base and made mounts for them, so if you have a specific gun in mind, they probably make a mount for it. BSA bases, for instance, are known to be very wide, so B-Square make a special mount just for them.

Now,I want tell you about an airgun I tested.It is a winchester 1000x and it seemed to be powerful.I kind of liked it for the price but do you recommend it?Im not buying it but my friend is and he needs to know.BB if you could make a post when you have a bit of a free time I would appreciate it.Thanks.

I have a thought about that. Have your friend test the gun and either you or he can post the results in the comments section of whatever post happens to be current. The time it will take me to obtain a Winchester 1000X would be at least six months, and you guys could have the job done in a few weeks. And I bet there are readers who will chip in with their observations, if you take the lead.

Along those lines, isn’t it about time for you to invest in a chronograph? The way you are going at this sport of airgunning, I have a feeling that a chrono would a be a nice tool to add to your range bag.

Tell your friend how to shoot a springer (you know how by now) and help him give his new rifle a good test!

I have the sidewheel for leapers scopes, but I was wondering is there some kind of material I can get that will replace the padding where it holds the parallex knob? I never really had it on tight but with the recoil it would come loose so in time the three screws wore down the ring of material where they touch the knob.

That material is a thin rubber sheet, as I recall. Have you asked Leapers for some of it? I think they might like to know what happened to your scope so they can improve on that feature, if it’s a problem.

I’ll get back to them, the pins that you screw in went through the rubber and scratched the knob abit but if I left them to loose when you line up the dots and you start to make an adjustment the wheel tends to turn before the parallex knob, you still get a finer adjustment when you look through the scope but the reading will still be more of an estimate just not off by much. It works great but to anyone that is getting one take it off the scope when your putting it in a case to transport it cause even the pressure of the foam will loosen it up.

What we do for transport is cut a matching hole in the foam opposite the wheel. I’ve done it to many of my FT hard cases. It’s scary the first time, but you can get replacement foam at a hobby shop, so it isn’t too critical.

Im going with the kodiaks because the exacts are out of stock.Still there are 2 types of kodiaks.The one the says beeman kodiak and the one that says beeman kodiaks match.Wich one is better and wich one should I use for hunting?

Happy first anniversary! I hope just the first of many. I just wanted to thank and appluad you once again for all your wonderful writings. It’s is a daily routine for me to read your blog. You make my every weekday that much brighter and I thank you! Keep ’em coming.

Thanks for the info.I agree that this blog changes your routine.I come home and I turn the computer on to check whats new in this blog.I was so bored when BB whent away for a week!!!!!!!!!!.I could not find what to do!!!!!!!!!!!But I just love this blog so keep em comming BB.

I started with a Shooting Chrony, and whenever I have a problem with my main chrono (like dead batteries or I’m too lazy to set it up) I default to a Chrony again.

But I did discover thet it’s possible to get spurious readings with the Chrony if you angle the shot up or down through the screens.

I currently use an Oehler 35P chronograph, which is the best product on the market. I’ve chronoed number 6 lead shot (.12 caliber!) traveling 65 f.p.s. with the Oehler. That’s impossible for any other chrono on the market. Also, the Oehler has a clock speed of 4 megahertz, while machines like the Chrony oscillate at 100 kilohertz. They’ll all give you a number, but I trust the Oehler number the most.

Because I’m new to air gunning, I’ve done a lot of web-roaming seeking information. I’ve found that your site is the most consistantly instructive and informative. It is one of the two air gunning sites I visit daily. Selfishly, I wish you had weekend columns. And I continue to be astonished by breadth, depth and volume of your knowledge, which make your site such a valuable resource.

I hope your’re able to keep your blog going for a long time. And, is it too much to hope for that you plan to collect all this valuable information into a book?

Thank you for the post on storing pump up airguns, i really appreciate it.

oh yeah, a bit late but… happy anniversary. i’ve been reading ur blogs for a few months now, i even download all your blogs to my local disc so i can read it any time i want. a lot of knowledge i wont get elsewhere. thanks a lot.

btw, about my sharp, it comes with a trigger block behind the trigger, if i move the block in, the trigger can not be squeeze, so it cant fire.

so, i think it’s quite save…if i do store my sharp with air in it, will i damage it?cause i’ve been doing that for quite some time

You won’t hurt your gun by storing it with air but the safety issue is still a problem. The trigger is not the problem. The linkage that runs from the trigger to the valve can operate on its own without the trigger being pulled.

That said, I have never had a problem like this with an Sharp gun. I do believe their mechanisms are designed to be safer than other blow-off valve guns.

B.B.,My maximum “pop can range” is 20 yards, and so for the first time, I need to scope. And since the IZH61 is my first springer, I was wondering if ring honing was neccisary on one as it is on many firearms? I am thinking no, as the recoil is similar to a .22 rimfire, which do not need it to prevent scope damage.And as an aside, I think putting “No e-mail replies” up under “There are no stupid questions” might help dicourage them, as you don’t want to be a site crawled by account finders for spam. Giving them out on public forums is a bad practice, And returning here is as easy as checking an account, not to mention far more fun!.357

Thanks, I have contacted Pyramid and am waiting for their response. Maybe the one I got is defective. When it is in the “R” position the recticle is illuminated green and visa-versa in the “G” position. I’m debating rather to get the same scope or one without the illuminated recticle, which leads me to another question…

Considering that I have fixed mounts would the rifle be more accurate and/or easier to zero if I chose a scope with a 32 or 40 Mil-Dot recticle on medium mounts, instead of a 50 Mil-Dot on high mounts? To me it seems like it would be easier to zero since the scope is closer to the rifle on medium mounts.

I was wondering what the best (and least expensive) scope would be for a RWS 48. I’ve read that that the heavy recoil is bad for most scopes and am wondering if my Bushnell Sportsman will be able to handle it. Thanks, Some Random Person

First, thank you so much for your blog. It’s been the best source of information during my research in choosing my first adult air rifle – a Gamo CFX with a Leapers Bug Buster 2 scope.

My question concerns adjusting the parallax of the scope for use at different ranges. I’ve done much research within your blog, the pyramid site and elsewhere about using AO and sighting scopes, and I’m doing my best to practice with the scope on my own. As a city dweller, my shooting spots are mostly indoors, and are limited currently to 20 yards and under. With the scope sighted in at that range and correctly focused, I got 1/2″ 5-shot groups, but can’t seem to do any better at under 10 yards from the same shooting position.

Shouldn’t I expect to tighten my groups at closer range? Or am I just having trouble focusing the scope for parallax (as it becomes more of a problem at closer ranges)? Also, am I correct in assuming that AO scopes are made to keep shots relatively on target vertically (through pellet’s flight) when they are focused for different ranges?

Mostly, I’m just trying to understand my equipment as best I can. I’m having a fantastic time, and your advice deserves a lot of the credit.

Also per your suggestions, I’ve correctly focused the reticle, and I alwyas check for parallax (reticle movement versus the target). Incidentally, when I DO nail a parallax free sight picture, the markings on the scope don’t really correspond to the actual measured shooting distance. When the target is placed at 20 yards, the scope actually reads around 30. ‘Sorry about the loads of questions.

I shoot sitting at a table with the gun supported on a gel rest ontop of a rigid support.

Oh, and I’ve found an amazing site with interactive animations that will really help your explanations on parallax and optics, pellet flight paths, spring gun physics, trigger mechanisms, etc. Scroll down to see them: http://www.arld1.com/

I think we may have the problem. You can’t rest most spring guns on anything except the flat of your open palm. Even the gel bag isn’t right for most spring guns. It has to be a hand. You can rest your hand on the bag.

At 10 yards, you should get one hole groups measuring under a quarter-inch center to center. Do you know how to measure that?

Hold the rifle loose, so it is free to recoil as much as it can. You are nothing but a platform.

Try this and let me know how it goes.

The scope reading differently changes with the temperature and all scopes do it. That’s why field target shooters put white tape around the numbersa and write in the actual measurements after range testing.

Hand: Thanks, B.B., I’ll try it. But I’m confused – you wrote to The.Man on 1/1/07 in the CFX review comments that “In your situation I would try the gel shooting support Pyramyd sells. You’d rest it on the railing with the gun on top.” This is essentially what I’m doing. Is this very different from what you tried in your review (“I also tried something that usually doesn’t work – I rested the gun DIRECTLY on a sandbag without a hand in between.), with no hand?

Measure:Yes – CTC of widest spread

Scope:OK, I already began to do this on my own. I look forward to see how the scope behaves in different environments.

You are reading everything and that’s good. I’m suggesting this because you are having a problem and I’m not there with you to analyse the problem. So I’m going through the possible causes for inaccuracy one at a time.

Have you tightened all the screws that hold your rifle in the stock (two triggerguard screws and two forearm screws)? That can be a problem, too.

I may ask you to clean your barrel with JB Bore Compound, which will be a big chore with your rifle because of the rotary breech. Crosman Permiers often leave lead deposits that caqn affect accuracy.

Screws:Nope, I’m planning on getting some gunsmith tools to check those out. Are the two in the forearm under the rubbery grips on either side?

Cleaning:I plan to do this too. I’ve read all your advice, and I’m compiling a shopping list. My only question is how to use patches, since I can’t draw them through from the breech. Would I push them in from the muzzle? Yikes. I also plan to look into lubing Premiers. I’ve read your advice on that too.

And just to remind you, I said in my initial post that I am getting < 1/2" groups at 20 yards, I just haven't been able to do better at 10 yards with the same set up. It's possible that this whole problem is all mental, in that I don't concentrate as much when the target is closer 🙂 I'll get back to you.